1. Field of the Invention
This invention relates to a lightweight structural panel having a honeycomb aramid core which is faced with a resin-impregnated fiber layer. More particularly, the invention concerns such a panel having significantly increased peel strength between the facing layer and the core and a process for making the improved panel.
2. Description of the Prior Art
A lightweight structural panel, having an aramid honeycomb core faced with a resin-impregnated fiber layer is known. Such panels have been used in aircraft for lightweight structural members, such as floorings, window panels, overhead luggage storage bins, and the like. Panels having high strength and stiffness have been made with facing layers in the form of resin-impregnated woven fabrics or cross-laid, unidirectional tapes made from high-strength, high-stiffness yarnsof poly(p-phenylene terephthalamide), fiberglass, or carbon. For aircraft-interior applications, a phenolic resin is usually used for the facing impregnant because of its low emission of smoke and toxic gases under fire conditions.
In manufacture of the above-described panels, the facing layer is adhered to the aramid honeycomb core by activation and curing of the resin. Only a small fraction of the honeycomb cross-section consists of solid material. The solid material is only in the walls which form the cells of the honeycomb. Thus, there is very little area on the surface of the honeycomb core to which the impregnated-fiber facing layer adheres. Because of the small area available for adhesion, the peel strength between the facing layer and the aramid honeycomb core of the above-described panels often is less than desired. Accordingly, an object of the present invention is to provide such a panel with increased peel strength between the core and the facing.